I personally have a lot of fun with this puppy. It is pretty cheap 2nd hand so it is worth considering. I would not recommend it if you are say, with a country band and looking for realistic sounds. However, if you are into industrial or weird ass sounds (like I am) then this unit can quite useful. The OS is fairly simple to get around, has lots of dedicated buttons and and works OK as a controller (minus the concerns above). I like thatyou can intentionally stick notes whereas some synths (i.e. Korg WS for instance) automatically send out NOTE OFF messages when you switch a channel. The sound quality can be gritty at times (I like that) and sounds "click" when you switch between them if you are using effects (I guess from switching in the new effect algorithm). The effects available are delay, reverb, distorion, chorus (I think) and some multi versions of the above. All in all, definitely worth the money if you put in some time to make your own sounds.

GilesW Used with a sequencer everything seemed sloppy. This is confirmed in Multi mode when you start playing stacked sounds. The K4 takes about 1.5 secs to stop.I sold mine because the processor was obviously under-powered.

Comments About the Sounds:
This a strange little beast. It does a mediocre job of instrument emulation if you aren't trying to do a professional score. The sample set tries to cover all bases at once but just doesn't cut it for most "realistic" sounds. That is not to say that this unot sounds terrible, not by far. It is just way better as a strange sound machine. The digital resonant filters are very very cool (if somewhat coarse) and the effects section helps somewhat (especially the distortion). The AM capability is kind of weak (unfortunately) and doesn't make that much difference normally. However, this machine does really excel at making weird noises, analog like bleeps and basses and strange percussive sounds. It has the most retarded envelope structure (i.e. way too fast so no pads) I have seen but otherwise is set up ok. Only other gripe is that the MOD and PB wheels ignore the local off command so when you use this keyboard to control something else, it will follow the MOD and PB settings locally as well.